Now let's move to our next case.
A 21 year-old man with a history of type 1 diabetes
presents to the clinic with 6 months of diarrhea.
He has had malodorous, loose stools about
4 to 5 times a day for the past 6 months.
Since the diarrhea began, he has
lost 3 kgs unintentionally.
He has no fevers, recent travel, abdominal
pain or blood or mucus in his stools.
On exam, vitals are normal, he appears thin.
His abdomen is soft and non-tender.
Labs show a hemoglobin of 11 with a
mean corpuscular volume or MCV of 105.
So the question is, what diagnostic
test should be done next?
Before we answer that, let's
look at some key clues here.
So, he has a history of type 1 diabetes
which is a history of autoimmune disease.
He does have chronic diarrhea
with unintentional weight loss.
And in this case, he has
an anemia that is macrocytic
so this might suggest a nutritional
deficiency in an appropriate clinical scenario.
So let's now talk about chronic diarrhea.
We can break down chronic diarrhea
into several different types.
The first type is called secretory diarrhea.
This distinguishing factor about secretory diarrhea
is that it occurs at all times of day and night.
So that's an important question you
should always ask your patients about.
The differential diagnosis for this
includes things like Carcinoid syndrome,
VIPomas and Zollinger-Ellison syndrome.
The next type of diarrhea is osmotic
diarrhea or for malabsorption.
This tends to be associated with eating
and because of that does not occur at night
and can be associated with an increased
stool osmotic gap which we will discuss later.
The differential diagnosis here is
quite broad but includes things like
lactose intolerance, pancreatic
insufficiency and Celiac disease.
The next type of diarrhea
Patients with inflammatory diarrhea
tend to have bloody and mucousy stools
and they may often have
fever or systemic symptoms.
The differential diagnosis here are
your types of inflammatory bowel disease
like Crohn's disease and ulcerative colitis.
Lastly, we have a
Patients with motility-related diarrhea often
have no alarm features and a normal colonoscopy.
An example of this type of disorder
is Irritable Bowel Syndrome.
So now that we've categorized different
types of diarrhea, let's now talk about
a diagnostic algorithm for helping you
differentiate between your broad differential.
So we begin with the patient
presenting with chronic diarrhea,
you want to first exclude
any of the things listed here.
So anything that can cause acute diarrhea -
lactose intolerance, irritable bowel syndrome,
a prior history of gastric or ileal resection,
a parasite infection, medications that can
cause diarrhea and any systemic diseases.
Keep in mind that much of this work
up you may be doing simultaneously.
Once you have done those things, you could
then send appropriate initial testing.
So this may include things
like a fecal calprotectin
which is an inflammatory
marker in the stool.
You can also check for occult blood
and you may also do a colonoscopy
or imaging of the small bowel
to further investigate.
If any of those things are abnormal, you should then work
up that patient for inflammatory bowel disease or cancer.
If they are normal on the other hand,
then we must do further testing.
So, that further testing involves
checking a stool osmotic gap.
We will discuss exactly what goes
into this measurement a bit later.
If you have an increased osmotic gap, the next
thing you wanna check is the fecal fat content.
If you have high fecal fat, this indicates
that the patient has a malabsorption syndrome
such as pancreatic insufficiency
or bacterial overgrowth.
If they have normal fecal fat, then
your differential includes things like
lactose intolerance, sorbitol
or lactulose or laxative abuse.
Now, if your patient had
a normal osmotic gap,
the next thing you can use to differentiate
between causes is a stool weight.
So, if they have a normal stool weight, this
makes your differential limited to things like
Irritable Bowel Syndrome
or factitious diarrhea.
If the stool weight is quite high or
greater than a 1000 grams in 24 hours,
this suggests that your patient may
have secretory laxative abuse.
So, we mentioned earlier a
A malabsorption syndrome is the inability to
absorb nutrients due to some underlying condition.
The most commonly involves the small
bowel because that's the location
where we absorb the majority
of the nutrients we take in.
So what are the mechanisms by
which malabsorption can occur?
There are several different
mechanisms that we'll review here.
The first is impaired mucosal absorption
as in Celiac disease or Whipple disease.
Next, you may have an issue with your brush border
enzymes, so such as in lactose intolerance.
If you have a problem with your pancreatic
enzymes or pancreatic insufficiency,
you may have chronic pancreatitis
or pancreatic cancer.
Next you may also have issues
with bile acid circulation.
An example of an underlying cause
here is an ileal resection.
And lastly, bacteria play a very large
role in helping us digest our nutrients.
So, when you have overgrowth of certain bacterial
species, you may also develop malabsorption.
An example here is small
intestine bacterial overgrowth.
So earlier, we also mentioned
a stool osmotic gap.
This is a simple measurement you can do by first
measuring the stool sodium and the stool potassium.
And then with this calculation, this will help you
differentiate between secretory and osmotic diarrhea.
When the stool osmotic gap is less than
50, this suggests a secretory diarrhea.
Between 50 and 125, this is an indeterminate
finding, so that is not quite helpful.
But if it is greater than 125, this helps
us because it suggests an osmotic diarrhea.
Let's talk a bit more specifically about one of
these types of malabsorption, Celiac disease.
Celiac disease is an immune mediated
reaction to gluten and gliadins in our food.
Patients tend to present with weight loss,
they may have fatty stools or steatorrhea
and because of their inability to absorb fatty
nutrients, they may also have nutritional deficiencies.
The diagnosis is done by testing
for specific antibodies.
So those are the anti-tissue transglutaminase
(TTG) or the anti-endomysial (EMA) antibodies.
The diagnosis can also be made
by endoscopy or colonoscopy.
Here, the features all point out here in our example
of histology from a patient with Celiac disease
is villous blunting, so
blunting of the villi,
and infiltration of lymphocytes
into the epithelium, as shown here.
The treatment is simply done by
avoiding gluten in the diet.
So now that we've previewed all of
that, let's return to our case.
A 21-year old man with a history
of known autoimmune disease
is now coming with chronic diarrhea,
unintentional weight loss.
and some of the clues in his labs
show that he has a macrocytic anemia
which might suggest
a nutritional deficiency.
In addition, one further clue is
that he has malodorous stools
which may be a sign of
steatorrhea or malabsorption.
So what diagnostic test
should we do next?
Because he is young and he has the
presence of another autoimmune condition,
you should suspect Celiac
disease in this case.
And the diagnosis can be made with
sending an anti-tTG antibody serology.